A Study On The De-noising Of The Passive Sonar Based On The Wavelet

Sonar technology is widely used to measure the depth of water, orientate, detect and identify the target, communicate under water, navigate, telecontrol, remote sense under the sea, search for gas and exploit the ores and so on. Since sonar equipments have many functions in naval ships, such as searching, detecting, orientating the target, the sonar equipments are thought important by navy. At the same time, sonar was also widely used in unmilitary field, such as measuring the depth or the space under water, Doppler velocimeter, detecting the shoal, supervising fishery, aid equipments of diving, orientation above or under water, communicating and remote sensing.But sonar signals often include all kinds of noises .How to get rid of them from signals and gain original sonar signals is the focus people care about.This paper focuses on the research of the de-noising of the passive sonar based on the wavelet. Based on the foundation of Matlab, this paper models and simulates the continuous spectrum and the line spectrum of ship radiated noise, figures out the propagation loss, adds the sea background noises, and at last synthesizes passive sonar signal of warship. On the basis of these, tradition waves filtering(mean filtering and EWMA(exponentially weighted moving average filtering)) are used to reduce noise in synthesized passive sonar signal of warship and the de-noising effect is gained .Then this paper decomposes and reduce noise in single step wavelet. By comparing the de-noising effect, this paper chooses exact wavelet basis .Then on the basis of wavelet basis of dB27, entropy of shannon is chosen out of all kinds of entropies of shannon, sure, norm, user and so on, and When threshold value from one to twenty, wavelet package hard threshold value, wavelet package soft threshold value is used to reduce noise and the effect is compared to that of tradition waves filtering(mean filtering and EWMA).At last it can be concluded that the best de-noising effect can be gotten on the condition of wavelet basis of dB27,entropy of shannon ,wavelet package soft threshold value of 17.Better effect can be gotten in de-noising of the passive sonar based on the wavelet. These methods have a significant foreground in de-noising of other target under water.